This invention relates generally to closure cap constructions, and more particularly to devices of this type wherein a captive closure cap part is turnably carried on a body part, and wherein the latter has an upwardly-facing cam track that is adapted to be engaged by an interior lug on the cap part in order to effect axially-outward movement of the latter as it is unscrewed.
A number of different cap constructions have been proposed and produced in the past, and have met with wide acceptance in the consumer marketplace. A typical patented construction is illustrated and described in U.S. Pat. No. 3,598,285, issued Aug. 10, 1971 to Morton B. Stull, and entitled CAPTIVE DISPENSING AND METERING CAP. This reference is believed to be the most relevant prior art of which applicant is aware.
This patented cap construction incorporates a base part and a screw cap part that is turnably carried on the base part. Both parts incorporate cooperable threads which effect axial movement of the cap part when it is turned. In addition, in order to provide a more positive advancing movement of the cap part when it is unscrewed, the body part incorporates a single cam track which is engaged by a lug disposed on the underside of the cap part. The lug is particularly shown in FIG. 6 of the patent, designated by the numeral 38. Alternate constructions are illustrated in FIGS. 8 and 9. In particular, FIG. 8 of the patent shows a cam track that has a non-uniform helical pitch, and wherein there is provided a bump or discontinuity part way up the track. As the consumer unscrews the cap part, he encounters a somewhat increased resistance to turning when the cap part arrives at the discontinuity. The purpose of incorporating this discontinuity in between the ends of the cam track was to provide to the consumer a means for accurately metering the rate of discharge of the container contents. Stated differently, the design was such that when the cap part lug arrived at the discontinuity, the discharge opening was of a pre-determined size intended to provide a calibrated, reduced flow rate compared to that which occured when the cap part was fully opened. In FIG. 9, the discontinuity takes the form of a small notch or recess part way up the track, and the objective was essentially the same, one of metering the flow rate.
Other patents involving captive screw cap constructions are U.S. Pat. Nos. 3,406,880; 3,407,967 and 3,433,394. The devices disclosed therein involve cooperable threads on a cap part and a body part in combination with single or double cam tracks disposed on the body part, and wherein concealed lugs on the underside of the cap part were intended to ride up the tracks in order to provide positive lifting force.
One of the problems which has arisen in constructions of the type noted above is that following assembly of the cap part to the body part, there is a tendency for the cap part to loosen as a result of vibration that is encountered during subsequent handling of the device. Very often such devices are assembled to containers by means of automatic capping equipment, which imparts turning movement to the base part in order to screw it onto the neck of the container. The torque applied to the base part was often transmitted to the cap part, sometimes causing inadvertent loosening or unscrewing. Under such circumstances it was necessary for assembly personnel to visually inspect the caps, and to manually close any which had inadvertently become partially open. In addition, during shipping and handling of the devices, similar problems involving loosening were sometimes encountered, resulting in loss of seal, product spillage, etc. Due to the nature of the plastic of which the parts was constituted, it was not possible to completely tighten the caps, as can usually be done with relatively stiff metal lids applied to rigid glass containers. Accordingly maintaining the twist cap in its sealed position during the filling, capping, and shipping of the dispenser in many instances presented a significant problem.